Yep. I think its peoples coping mechanism, so try and be gentle with her.
Something Ive learned about the elderly. Often, although they enjoy their lives, they are marking time. The older they get, the more of their friends they have lost. The more of themselves they lose. They aren't what they used to be, and any attempt to stop them is met with resistance. This resilience you're facing is often the reason they are living longer lives, so rather than fight it, assist them to take some precautions and continue as best they can.
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